(1) Field of the Invention
The present invention relates to an image forming apparatus, and particularly to an art of removing a graphite insulation film (hereinafter, carbon film) deposited on the outer circumferential surface of a commutator of a brush motor that drives a conveyance roller that conveys recording sheets.
(2) Description of the Related Art
An image forming apparatus includes a conveyance roller that conveys recording sheets each on which toner images are to be carried. The conveyance roller is driven to rotate by a brush motor, for example. The brush motor has the structure in which a brush is in contact with a commutator rotating together with a rotor such that an electrical power is fed from the brush to the commutator.
There is known that the use of a brush motor for a long period causes formation of a carbon film on a surface of a commutators due to spark discharge between a brush and the commutator. The carbon film needs to be removed so as to avoid the carbon film from hindering the electrical power feed from the brush to the commutator.
For this reason, with respect to a brush motor included in a disc playback device that moves an optical pickup, there has been proposed a conventional art of removing a carbon film deposited on the brush motor by applying a high voltage of 24 V or more for example to the deposited a carbon film to cause insulation breakdown of the carbon film (see Japanese Patent Application Publication No. 2011-18392).
According to this conventional art, a worm gear is attached to a rotor of the brush motor. There occurs a positional deviation between a brush and a commutator in the thrust direction (the axial direction of the worm gear), depending on the rotational direction of the rotor. Accordingly, a cleaning sequence is performed both while the rotor makes positive rotation and while the rotor makes reverse rotation.
When a high voltage is applied to the commutator from the brush so as to remove the carbon film, the rotational speed of the rotor increases. For this reason, according to the above conventional art, a cleaning sequence cannot be performed while audio playback operations are performed by positive rotation of the rotor. Accordingly the cleaning sequence is performed while audio playback operations are not performed. For example, in order to repeatedly play back music which has ended once, the brush motor drives the rotor to make reverse rotation so as to move the optical pickup to the start position of the track by. Application of a high voltage in this situation enables performance of a cleaning sequence by reverse rotation of the rotor.
However, in order to perform a cleaning sequence by positive rotation in the same manner as in the above reverse rotation, the brush motor needs to move the optical pickup in the direction opposite to the start position of the track. This causes a problem that the start of repeat playback is delayed.
Therefore, there is a possibility that if the above conventional art is applied to an image forming apparatus that includes a brush motor that drives a conveyance roller to rotate, the conveyance speed of recording sheets reduces, and this results in reduction in productivity of the image forming apparatus.